The mechanical properties reports on the Forest Products Laboratories site bear out my experience with E. red cedar and western red cedar: very wimpy wood. ERC is about half as stiff as POC and wrc is about 11/17 as stiff as POC.
If you leave them a full 3/8 diameter, they will still be pretty weak. If it were otherwise, all arrows would be made of western red cedar--it's plentiful and wonderfully straight.
JimDavis